Device for conveying sheets with rolls

Abstract: A paper transport system includes an apparatus (24) for controlling movement of the sheets (S₁,S₂) along the predetermined course (P) to provide sheet buffering. The apparatus (24) includes first (32) and second (34) friction surfaces mounted for movement in orbital paths on opposite sides of the predetermined course (P) in opposed relationship to define a nip (30) through which the paper sheets (S₁,S₂) pass. A selectively operable drive (40,42) is provided for independently controlling the movement of the first (32) and second (34) friction surfaces, and the first friction surface (32) has a coefficient of friction with the paper sheets (S₁,S₂) which is greater than the coefficient of friction of the second surface (34) with the paper sheets (S₁,S₂) which is in turn greater than the coefficient of friction between the paper sheets (S₁,S₂). In an alternative embodiment (Fig. 6), the friction surfaces are provided on corrugation feed rolls (68).

Description: The subject invention is directed to the art of paper sheet handling and, more particularly, to a sheet buffering system. In particular, the present invention relates to a sheet buffering apparatus which includes a pair of spaced apart guide members for defining a predetermined course to direct sheets seriatim along the predetermined course toward a buffering nip, and first and second friction surfaces mounted for movement in orbital paths on opposite sides of the predetermined course in opposed relationship to define said buffering nip through which the sheets pass, the first friction surface having a coefficient of friction with the sheets which is greater than the coefficient of friction of the second friction surface with the sheets which is in turn greater than the coefficient of friction between the sheets. Such a sheet buffering apparatus is known from JP-A-59 138 536. The invention is especially suited for use in the paper handling and transport system of an electrophotographic printing machine and will be described with reference thereto; however, as will become apparent, the invention could be used in many types of paper sheet handling systems in a variety of different machines. In electrophotographic printing machines, it is sometimes necessary or desirable to temporarily hold or delay the transport of individual paper sheets at various points in the paper path to provide additional time for downstream processing to be performed. Such temporary holding or delaying of sheets is generally referred to as "buffering and has been accomplished in many different ways. One prior art method of buffering is to temporarily slow or stop a roll nip or other paper transport for a period of time equal to the inter-copy-gap between successive sheets. Of course, this yields only a very short buffering time. If longer times are required, other systems must be used. For example, multiple path systems and systems which run sheets against stalled roll pairs or stop gates have sometimes been used. US-A-4,801,134 discloses a paper feed apparatus capable of feeding common use papers and specifically processed papers, comprising a feed out roller, a regular rotational roller for feeding out sheets one by one towards a conveying roller pair at a downstream position along a paper path defined by paper guides. US-A-2,979,330 discloses a sheet separating device for positively separating sheets of paper, comprising pairs of axles with corresponding sets of nearly abutting rollers, or a pair of axles provided with staggered sets of roller. There exists a need for a paper transport system which provides a simple and effective buffering system which uses only one paper path and maintains positive drive on the sheets at all times. The present invention provides a sheet buffering apparatus of the above-mentioned kind which is characterized by the pair of friction surfaces being selectively independently operable to stop movement of a first one of said pair of friction surfaces while moving a second one of said pair of friction surfaces to buffer a first sheet at said nip while impelling a second sheet into said nip. In particular present invention provides a paper transport system wherein paper sheets are moved seriatim along a predetermined course, comprising first and second friction surfaces mounted for movement in orbital paths on opposite sides of the predetermined course in opposed relationship to define a nip through which the paper sheets pass, selectively operable drive means for controlling the movement of the first friction surface, and the first friction surface having a coefficient of friction with the paper sheets which is greater than the coefficient of friction of the second surface with the paper sheets which is in turn greater than the coefficient of friction between the paper sheets. Preferably, each of the first and second friction surfaces is continuous throughout its respective orbital path. Preferably, each of the first and second friction surfaces has substantially constant friction characteristics throughout its full extent. Preferably, the drive means is capable of selectively stopping and reversing the direction of movement of the first and second friction surfaces about their respective paths of orbital movement. Because of the noted relationship between the coefficients of friction of the first and second friction surfaces, the apparatus allows two sheets to be stopped and held in the same nip and then fed out either independently or simultaneously. Note that when a first sheet is in the nip, the first friction surface can be stopped while the second friction surface continues to be driven. The first sheet will, however, be stopped and frictionally held by the first friction surface. A second sheet can then be fed between the stopped first sheet and the second friction surface. By then stopping movement of the second friction surface, both the first and second sheets are held in the nip. Alternatively, by selectively driving both or a selected one of the friction surfaces, both or a selected one of the sheets can be driven from between the nip. In accordance with a further aspect of the invention, there is provided a method of controlling the movement of paper sheets in a sheet transport system wherein the sheets are moved seriatim along a predetermined course of movement. The method comprises providing along the predetermined course of movement a nip through which the paper sheets are passed, with the nip being defined by opposed first and second friction surfaces mounted for movement in orbital paths. The first friction surface is selected to have a coefficient of friction with the paper sheets which is significantly greater than the coefficient of friction of the second friction surface with the paper sheets which is, in turn, selected to be significantly greater than the coefficient of friction of the paper sheets with each other. The method further comprises driving the first and second friction surfaces in their orbital paths to cause the nip to impel sheets therethrough, and when it is desired to stop a first sheet traveling through the nip, stopping orbital movement of the first friction surface and maintaining it stopped at least until a second sheet enters the nip. The method preferably includes the step of directing the second sheet into the nip to a location between the first sheet and the second friction surface. The method may include the step of restarting orbital movement of the first friction surface after the second sheet is in the nip. The method may include continuing movement of the second friction in its orbital path after the orbital movement of the first frictional surface is restarted. The present invention further provides a method of controlling movement of paper sheets according to claim 11 of the appended claims. The method may further include the step (g) of urging a second sheet to travel against said trailing edge buckling member and toward said first nip while maintaining orbital movement of the first friction surface engaging said lead portion of the first sheet stopped. The method may further include the step (h) of urging a second sheet to travel against said trailing edge buckling member while simultaneously driving the first friction surface in its orbital path causing the nip created thereby eject the first sheet from the sheet buffering apparatus. Preferably, the step (g) includes the step (g(i)) of receiving said second sheet between the first sheet and said second friction surface. The method may further comprise the step (j) of engaging a trailing portion of the second sheet with said trailing edge buckling member urging said trailing portion of the second sheet out of said predetermined course of movement. The present invention further provides a paper sheet buffering apparatus according to claim 12 of the appended claims. Preferably, the urging means comprises a spring member for urging the trailing edge of the first sheet into the baffle means. Preferably, the first movable friction surface means has a second coefficient of friction with the copy sheets which is greater than the first coefficient of friction for selectively impelling the first copy sheet along the copy sheet path; and the second movable friction surface means has a third coefficient of friction with the copy sheets which is greater than the first coefficient of friction and less than the second coefficient of friction, for selectively impelling the second copy sheet along the copy sheet path. The selectively operable drive means may include means for stopping movement of the second movable friction surface means to buffer the second copy sheet at the guide means with the trailing edge of the second sheet in said baffle means while a third copy sheet is passed into the guide means between the urging means and the second copy sheet. The present invention further provides a method of sheet buffering according to claim 13 of the appended claims. Preferably, the step (A) includes defining a curvilinear sheet travel path. Preferably, the step (B) includes the step of bending the first sheet with said curvilinear sheet travel path; and the step (C) comprises releasing said first sheet from said bending after said trailing edge is released by said first nip and releasing said trailing edge from said sheet travel path. The step (A) of defining said curvilinear sheet travel path may include the steps of (A1) defining a first sheet travel path portion tangential to said first paper feeding nip in a first direction by providing said first paper feeding nip in a first orientation; and (A2) defining a second sheet travel path portion tangential to said second paper feeding nip in a second direction by providing said second paper feeding nip in a second orientation different from said first orientation. The step (A) may include providing at least one curved sheet guide member between said first paper feeding nip and said second paper feeding nip defining a curvilinear sheet travel path. Alternatively, the step (B) may include the step of bending the first sheet against said at least one sheet guide member in substantial conformity with said curvilinear sheet travel path; and the step (C) may include the step of relaxing the trailing edge from said bending into a baffle on said at least one sheet guide member. In addition, step (A) may include providing spaced apart guide members between said first paper feeding nip and said second paper feeding nip. The step (C) may include the step of urging the trailing edge against a first of said spaced apart guide members using a spring member on a second of said spaced apart guide members. The present invention further provides a sheet buffering apparatus according to claim 14 of the appended claims. The sheet buffering apparatus may further comprise means in said guide system for defining a first sheet travel path portion in a first direction upstream of said buffering station; and means in said guide system for defining a second sheet travel path portion in a second direction different from said first direction downstream of said buffering station. The sheet buffering apparatus may further include means for urging said trailing edge of said first sheet away from said sheet path. Preferably, the means for urging comprises a curved portion of a second guide member of said spaced apart guide members. The sheet means for urging may comprise a spring member on a second guide member of said spaced apart guide members, and preferably on a curved portion thereof. The buffering station may comprise a step formed in said first guide member of said spaced apart guide members for positioning said trailing edge of said first sheet laterally entirely off of said sheet path permitting said second sheet to be received along said sheet path avoiding contact with said trailing edge of the first sheet. The present invention further provides a method of sheet buffering according to claim 15 of the appended claims. The method may further comprise providing a first guide member of said spaced apart guide members with an expanded step portion defining a sheet buffering station receiving said trailing edge of said first sheet moved out of said sheet travel path. Preferably, the step (H) includes the step (H1) of urging the first sheet into the step portion of the first guide member of said pair of second apart guide members. The step (H1) may include urging the first sheet into the step portion with a second guide member of said pair of spaced apart guide members. The step (H1) may include the step of urging the first sheet into the step portion with a spring member on a second guide member of said pair of spaced apart guide members. The step (I) may include the step of feeding the leading edge of the second sheet in between said trailing edge of the second sheet in between said trailing edge of said first sheet and said second guide member of said pair of spaced apart guide members. The step (I) may include the step of feeding the leading edge of the second sheet in between said trailing edge of said first sheet and said second guide member of said pair of spaced apart guide members. For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following drawings, in which: FIGURE 1 is a schematic elevational view of a portion of a paper transport system incorporating the invention; FIGURES 2 to 5 are partial schematic elevational views similar to FIGURE 1 but showing a possible sequence of steps in using the apparatus of FIGURE 1; FIGURE 6 is a schematic showing of a modified form of sheet buffering system useful for understanding the invention; FIGURE 7 is a side elevational view of the FIGURE 6 embodiment; FIGURES 8 to 12 are identical side views of key portions of a sheet buffering system useful for understanding the invention, showing sequential steps in the operation thereof; and FIGURES 13 to 15 show three alternative upstream feeder modifications of the buffer system of Figs. 8 to 12. In the drawings, like reference numerals have been used throughout to designate identical elements. FIGURE 1 schematically depicts a portion of a sheet transport system having a sheet buffering arrangement according to the invention incorporated therein. The system shown in FIGURE 1 is specifically intended for use in an electrophotographic printing machine; however, the apparatus and system could clearly be used in a variety of other types of equipment incorporating sheet handling and transportation systems. Broadly, as illustrated in FIGURE 1, the apparatus generally comprises guide means which define a predetermined course of paper movement or path indicated generally by the dash dot line P . In the preferred embodiment, the guide means comprise a spaced pairs of respective upper and lower guide panels 12 and 14 , respectively, which direct sheets to a first pair of horizontally positioned driven rolls 16 and 18 , respectively. The rolls 16 and 18 are positioned in opposed relationship and driven in the direction of the arrows to define a first drive nip 20 . The buffering station 24 is located immediately downstream of the drive rolls 16, 18 and includes upper and lower sheet guides 26 and 28 which are positioned in spaced opposed relationship and arranged to direct sheets coming from the drive nip 20 downwardly into the nip 30 of a second pair of spaced rolls 32 and 34 , respectively. Sheets passing through the nip 30 are received and directed along the predetermined path of paper movement to subsequent use or processing equipment (not shown) by suitable guide means in the form of guide plates or panels 36 and 38 . For reasons which will subsequently become apparent, the rolls 32 and 34 are each provided with separate drive means capable of independent operation. Also, roll 32 is equipped with a braking means. In the FIGURE 1 showing, the drive means are depicted schematically and could comprise any standard type of drive motor. As illustrated, roll 32 is provided with a first independent drive means 40 , the roll 32 having an associated brake. Roll 34 is driven in a similar manner from an independent drive means 42 . The drive means 40 and 42 are controlled in a manner subsequently to be described from a main controller unit 44 . Suitable sheet sensors 46 and 48 are positioned immediately downstream of the rolls 16 and 18 to detect the presence of sheets entering the buffering station 24 . The system and apparatus shown in FIGURE 1 allows two sheets to be stopped in the buffer station 24 and held in nip 30 and then fed out either independently or at the same time. While this function is being carried out, the system maintains a positive drive on the sheets at all times. To accomplish this function and result, the system is arranged so that the rolls 32 and 34 have a particular relationship in their coefficient of friction relative to the paper being handled. Specifically, the roll 32 is a high friction roll and has a coefficient of friction relative to the paper being transferred which is higher than the coefficient of friction of roll 34 relative to the paper being transferred, and both rolls have their coefficient of friction selected so that they are higher than the coefficient of friction of the paper to paper. Although many different materials could be used to form the rolls 32 and 34 to have the required relative coefficient of friction, in the subject embodiment, the low friction roll 34 is made of microcellular urethane with a coefficient of friction to paper of approximately 1.2, and the high friction roll 32 has a surface coating of an RTV silicone with a coefficient of friction to paper of approximately 2.5. The soft, compressible nature of the microcellular urethane yields a wide nip zone. This distributes the nip force over a large area resulting in low pressures that minimize the forces that can cause image smear. With the rolls 32 and 34 having the relative coefficient of friction in the ranges as described, the system can be operated generally in the manner best understood by reference to FIGURES 2 to 5. For example, as shown therein, a first paper sheet S 1 is driven into the buffering nip 30 by being directed thereto from rolls 16 and 18 . At the time the sheet S 1 is directed to the buffering nip 30 , both rolls 32 and 34 are being driven from their respective drive means 40 , 42 . As the trailing edge of the sheet S 1 passes the sensors 46 , 48 , the controller 44 acts to stop the driving movement of roll 32 (the roller having the highest coefficient friction relative to the paper). Also, the brake (not shown) is simultaneously actuated to hold roll 32 in its stopped position. Roll 34 continues to be driven but the sheet S 1 remains stationary in the position shown in FIGURE 3 because of the significantly higher coefficient of friction between the sheet and the stopped roll 32 . Of course, the driven roll 34 merely continues rotating and slips on the surface of sheet S 1 . It should be noted as shown in FIGURE 3 that when the sheet S 1 has moved to the stopped position, the trailing edge is preferably in an upper or raised position as permitted by the shape of upper guide plate 26 and the action of a Mylar leaf spring (not shown). This places the first sheet S 1 in a position such that the second sheet to enter the buffering station 24 from rolls 16, 18 will enter a position beneath sheet S 1 . This is shown in FIGURE 4 wherein the second sheet S 2 is engaged between the driven roller 34 and the first sheet S 1 . Because of the relationships between the various coefficient of friction, the sheet S 2 is driven along the path and slides along on the first sheet S 1 which maintains its stationary position against the stopped roll 32 . With the second sheet S 2 fed into the nip 30 , both rolls can be actuated to drive both sheets S 1 and S 2 out of the buffering station simultaneously. Alternatively, it is, of course, possible to maintain roll 32 in its stopped position and merely drive the second sheet S 2 through nip 30 while maintaining sheet S 1 in its stopped position. Of course, it is also possible to stop roll 32 for a predetermined period of time to hold both sheets S 1 and S 2 in position in nip 30 . Thereafter, the rolls 32, 34 can be actuated to drive either or both of sheets S 1 and S 2 from the nip 30 . FIGURES 6 and 7 show examples useful for understanding the invention wherein a single set of drive rolls in combination with superposed idler rolls can hold a first sheet while a second sheet is driven into the nip between the driven and idler rolls. More particularly, as illustrated, the FIGURE 6 embodiment includes a first set of opposed rolls 54 and 56 which define a feed nip and are driven in the direction shown to feed paper sheets S 1 and S 2 along the path 58 to a buffering station 60 . The buffering station 60 includes support and guide baffles 62 and 64 which confine the sheets moving along path 58 and direct them into the corrugation roll arrangement 66 . The corrugation roll arrangement 66 comprises a lower set of rolls 68 that are driven from a suitable drive 70 . A superjacent set of idler rolls 78 are positioned so that individual ones of the idler rolls 78 are axially intermediate the drive rolls 68 and slightly interleaved therewith to cause the sheets S 1 ,S 2 therebetween to be corrugated and gripped. In operation, the first sheet S 1 to enter the buffering station 60 is stopped at the location shown by stopping the corrugation drive rolls 68 . These rolls have the high coefficient of friction and preferably have the construction as described relative to rolls 34 of the FIGURES 1 - 5 embodiment. The first sheet S 1 is thus held in the position shown, as the second sheet S 2 enters the buffering station 60 . With sheet S 1 held in position, second sheet S 2 is driven into the corrugation nip between sheet S 1 and the idler rolls 78 . When the second sheet S 2 is substantially even with sheet S 1 , the controller actuates the drive rolls. Both sheets S 1 and S 2 are then driven through the corrugation nip since sheet S 2 is loaded against sheet S 1 by the idler rolls 78 . This generates a positive drive force on the sheets, yet little drag force. Figures 8 to 12 show a buffer system 11 for a printer. The buffer system 11 is given as an example which is useful for understanding the present invention, and has main sheet output path 12 defined by a downstream upper baffle 13a, an upstream upper baffle 13b, a downstream lower baffle 14a, an upstream lower (buckling) baffle 14b, a downstream feed nip 16 (or 15) at the downstream end, and an upstream feed nip 22 at the upstream end. There is less than one sheet dimension between these two feed nips 16 and 22. A buckle chamber 30 starts just downstream of nip 22, and is shown between upper baffle 13b and 13a in this example. Alternatively, the buckle chamber 30 can be below the main path 12, as discussed herein. The buckle chamber 30 provides a substantially opening away from the main sheet path 12 for a sheet buckle to form therein. As shown in the examples of Figs. 13, 14 and 15, several feeder alternatives can be used for the upstream drive nip 22 to even better ensure that the trail edge of the first sheet 18 is so buckled positively and correctly. Although conventional feed nips 22 with rollers 22a may be used, as shown, various configuration variations for the upper roll of the upstream feed nip 22 are possible to assist buckling. In Fig. 13, foam rolls 22b are inter-positioned between the upstream nip 22 normal elastomer upper drive rolls 22a. In the alternative of Fig. 14, small paddle-blades on rolls 22c (toothed rolls) are positioned between the normal upper drive rolls 22a. In the alternative of Fig. 15, a small toothed belt 23 is used to provide a continuous driving surface and ensure that the tail edge of the sheet is driven into its buffer position correctly.

Claims: A sheet buffering apparatus (24; 60) which includes a pair of spaced apart guide members (26, 28; 62, 64) for defining a predetermined course (P) to direct sheets (S 1 , S 2 ) seriatim along the predetermined course (P) toward a buffering nip (30), and first and second friction surfaces (32, 34; 68, 78) mounted for movement in orbital paths on opposite sides of the predetermined course (P) in opposed relationship to define said buffering nip (30) through which the sheets pass, the first friction surface (32; 68) having a coefficient of friction with the sheets (S 1 , S 2 ) which is greater than the coefficient of friction of the second friction surface (34; 78) with the sheets (S 1 , S 2 ) which is in turn greater than the coefficient of friction between the sheets, characterized by the pair of friction surfaces (32, 34; 68, 78) being selectively independently operable to stop movement of a first one of said pair of friction surfaces (32) while moving a second one of said pair of friction surfaces (34) to buffer a first sheet (S 1 ) at said nip (30) while impelling a second sheet (S 2 ) into said nip (30). The sheet buffering apparatus as set forth in claim 1, further comprising a pair of selectively operable drive means (40, 42) for independently controlling the movement of said pair of friction surfaces (32, 34). The sheet buffering apparatus as set forth in claim 2, the pair of selectively operable drive means (40, 42) being adapted to selectively stop and reverse a direction of movement of said first one of said pair of friction surfaces (32) and said second one of said pair of friction surfaces (34) about their respective paths of orbital movement. The sheet buffering apparatus as set forth in claim 1, said pair of guide members (26, 28) being curved to define a predetermined curvlinear course of sheet movement (P), and a first one of said pair of guide members (26) including a step region defined therein for positioning a trailing edge of said first sheet (S 1 ) laterally off said predetermined curvlinear course of sheet movement (P) permitting said second sheet (S 2 ) to be received along said predetermined curvlinear course (P) of sheet movement avoiding contact with said trailing edge of said first sheet (S 1 ). The sheet buffering apparatus as set forth in claim 4, a second one of said pair of guide members (28) including a spring member for urging said trailing edge of said first sheet (S 1 ) laterally off said predetermined curvlinear course of sheet movement (P) and into said step defined in said first one of said pair of guide members (26).

Inventors: BARRIENTOS FRANCESCA A, DESANCTIS ANTHONY T, KAMPRATH DAVID R, MANDEL BARRY P, RIZZOLO CHARLES D, VANDONGEN RICHARD A, BARRIENTOS, FRANCESCA A., DESANCTIS, ANTHONY T., KAMPRATH, DAVID R., MANDEL, BARRY P., RIZZOLO, CHARLES D., VANDONGEN, RICHARD A.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1994
Main classification: B65H5
IPC codes: B65H9, B65H5, B65H29